Printer having a permanent magnet hammer mechanism

ABSTRACT

A PRINTER HAVING A HAMMER MECHANISM CONTAINING HAMMERS WHICH ARE SELECTIVELY AND ELECTRODYNAMICALLY ACTIVATED UPON SELECTIVE ENERGIZATION OF ACTIVATING COILS ATTACHED TO THE HAMMERS. EACH ACTIVATING COIL IS LOCATED BETWEEN A PAIR OF POLE PIECES OF OPPOSITE POLARITIES WHICH ABUT THE OPPOSITE POLES OF A THIN PERMANENT CERAMIC MAGNET MAGNETIZED THROUGH ITS THIN DIMENSION. THE MAGNETS ARE U-SHAPED AS ARE THOSE POLE PIECES ABUTTING THE OUTSIDE SURFACES OF THE MAGNETS. EACH HAMMER COMPRISES AN ACTIVATING AND A PELLET PORTION DISPOSED AT AN ANGLE TO EACH OTHER AND SUPPORTED WITHIN THE HAMMER MECHANISM BY A U-SHAPED SPRING. EACH LEG OF THE U-SHAPED SPRING SUPPORTS AND IS LOCATED PERPENDICULAR TO ONE PORTION OF THE HAMMER.

Sept. 21, 1971 A NYMAN HAL 3,606,834

PRINTER HAVING A PERMANENT MAGNET HAMMER MECHANISM Filed June 24,- 1969 3 Sheets-Sheet 1 FIG.|

mvsmons ALEXANDER NYMAN ROBERT H. CURTISS 7/{wa/ ATTORNEY Sept. 21, 1971 Nmm ETAL I 3,606,834

PRINTER HAVING A PERMANENT MAGNET HAMMER MECHANISM Filed June 24, 1969 s, Sheets-Sheet n United States Patent O US. Cl. 101-93 9 Claims ABSTRACT OF THE DISCLOSURE A printer having a hammer mechanism containing hammers which are selectively and electrodynamically activated upon selective energization of activating coils attached to the hammers. Each activating coil is located between a pair of pole pieces of opposite polarities which abut the opposite poles of a thin peranent ceramic magnet magnetized through its thin dimension. The magnets are U-shaped as are those pole pieces abutting the outside surfaces of the magnets. Each hammer comprises an activating and a pellet portion disposed at an angle to each other and supported within the hammer mechanism by a U-shaped spring. Each leg of the U-shaped spring supports and is located perpendicular to one portion of the hammer.

BACKGROUND OF THE INVENTION This invention relates to printers and, more particularly, to printers having hammer mechanisms containing hammers activated by electrodynamic forces, i.e., forces exerted by magnetic fields on electrical conductors positioned at right angles to the fields.

Numerous printers have been developed for printing the output of data processing apparatus. Generally, in these printers one or more print hammers strike a printing medium and ribbon against type characters on a drum of chain revolving at high speed. The printing medium is successively advanced after each line is printed. Actvation of the hammers is timed with respect to the drum or chain such that the desired type characters are impacted.

Some of these printers utilize electrodynamic forces to activate their hammers. An activating coil is attached to each hammer and located in a magnetic field; the hammers are selectively activated by selectively energizing the coils. When energized, each coil develops a second magnetic field which interacts with the one within which it is located and moves the coil and its attached hammer. However these printers are generally complex and relatively expensive. In addition, when the magnetic field is produced electrically, rather than by permanent magnets, a certain amount of time is required for a field of sufficient strength to be generated and the printing speed is decreased accordingly.

Some printers having electrodynamically activated hammers use a pair of parallel leaf springs to support each hammer. The springs allow movement of the hammers toward and away from the printing medium, yet support the hammer in all other directions.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a printer having electrodynamically activated hammers and which is uncomplex, inexpensive, reliable, economical to operate, and easy to repair.

It is another object to provide a printer utilizing permanent magnets to activate its hammers.

It is another object to provide a printer utilizing permanent magnets to activate its hammers with a minimal loss of magnetic flux.

3,606,834 Patented Sept. 21, 1971 ICC It is a further object to provide a printer whose hammers each comprise two portions disposed at an angle to each other and which is supported in a hammer mechanism by a spring member which allows the two portions to move in dilierent directions when the hammer is activated.

According to the invention, these and other objects are achieved by a printer having a hammer mechanism containing hammers attached to activating coils which are crossed by magnetic fields such that the hammers are selectively and electrodynamically activated by selectively energizing the coils. The magnetic fields are provided by permanent magnets having their opposite surfaces of opposite polarities. Each magnet is interposed between and abuts a pair of pole pieces which also straddle an activating coil.

In the preferred embodiment, each hammer is made up of two portions disposed at an angle to each other and supported within the hammer mechanism by a member having flexible legs. Each leg supports and is located perpendicular to one portion of the hammer, thus allowing the two portions to move in different directions when the hammer is activated.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view of a preferred embodiment of the printer.

FIG. 2 is a perspective view of a typical portion of the hammer mechanism in the printer shown in FIG. 1.

FIG. 3 is a schematic block diagram of a control circuit for the printer.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 schematically illustrates a printer having a conventional print drum 1 with rows of type characters on its periphery. The drum is rotated by a driving means not shown. Paper 2 is advanced to a location adjacent the drum and across a line extending along the drums length where printing occurs, i.e., the print line. A pair of con ventional tractors, 3 and 4, having toothed endless belts 5 which engage perforations in the paper advance the paper an increment each time another line is to be printed. Each belt revolves around a pair of rollers, 7a and 717, one of which is driven by a means not shown.

Referring to FIGS. 1 and 2, a hammer mechanism 8 is positioned adjacent the drum 1 at the print line. A plurality of hammers 9, in groups of four, are provided within the hammer mechanism and extend along the drum. The hammers are supported by essentially U-shaped springs 10 mounted within a frame 11, each hammer being supported by one of the springs. An electrically energizable activating coil 12 is attached to each hammer. One half of each coil is placed within a magnetic field generating means which extends along the drum and provides magnetic lines of force such that energization of each coil activates its attached hammer. When activated, each hammer bends its attached spring 10 and impacts the paper 2, a print ribbon (not shown) and a type character on the drum 1.

The magnetic field generating means consists of three spaced pole pieces: two north pole pieces 13 and a south pole piece 14 interposed between the north pole pieces. Between each pair of adjacent pole pieces a permanent magnet 15 is placed abutting the two. The magnets are constructed of any of the well-known ceramic magnetic materials. They are thin members magnetized through their thin dimensions such that their opposite poles are on their opposed surfaces. The magnets are placed as shown with their like poles facing each other and no pole piece is abutted by surfaces of opposite polarities. The magnets are U-shaped as is each pole piece abutting the outside surface of a magnet. The north pole piece in the center only abuts the inside surface of the inner magnet and is of the shape shown. The pole pieces extend past the ends of the magnets and one half of each activating coil 12 is located in the air gap formed between adjacent pole pieces. Such a U-shaped arrangement keeps loss of magnetic flux to a minimum since a pole piece abuts the entire pole of each magnet and the flux is concentrated at the activating coils. During construction of the magnetic field generating means, each ceramic magnet may be formed by three mating parts: one part being the base of the U and the other two parts being the Us sides.

Referring in particular to FIG. 2, one group of four hammers is shown. Each coil 12 having leads 16 is attached to a hammer with one half of it projecting in the air gap between two adjacent pole pieces. Magnetic lines of force travel across the gap between each pair of adjacent pole pieces and the coils 12 are wound in planes substantially perpendicular to the magnetic lines of force. Current in that half of each coil located between the pole pieces and crossed by magnetic lines of force essentially travels in a single direction parallel to the pole pieces. Therefore, energization of the coils moves them perpendicular to both the direction of this current and the magnetic field. The hammers are thus moved either toward or away from the drum depending on the currents direction.

The magnetic lines of force within each of the air gaps move in a direction opposite to the lines of force in the air gaps directly above and beneath it. Therefore, to activate the hammers so that they move toward and impact the drum, each coil is energized in the appropriate direction opposite to that in which the coils in the air gaps above and beneath it are energized. For example, applying the left-hand rule, the coil in the bottom air gap is energized in a counterclockwise direction while the coil in the air gap directly above the bottom one is energized in a clockwise direction. The coils 12 in each group of four hammers are positioned in a staggered arrangement such as the one illustrated to reduce the possibility of the coils being crossed by magnetic line of force generated by the energization of adjacent coils.

The hammers 9 are made of two portions: a metal pellet portion 17 which impacts the paper, and an activating portion 18 made of plastic. So that all the pellet portions '17 may be arranged along the print line while the coils are located in their respective air gaps, each activating portion 18 is disposed at an angle to its pellet portion. The coils are substantially flat and partially embedded in one end of the plastic portion. The plastic portions 18, like the coils, are located in planes substantially perpendicular to the magnetic fields and parallel to the pole pieces. The U-shaped springs 10 are secured to the frame 11 by fasteners 19. When energized to activate its hammer, each activating coil is forced along the plane of the plastic portion 18 of a hammer and out from between the pole pieces. The legs 10a of the U- shaped springs 10 are bent and the pellet portion 17' of the hammer impacts the paper 2. Each leg 10a of a spring 10 supports one of a hammers two portions and is located perpendicular to the portion of the hammer to which it is attached.

As previously noted, the activating portion is in the same plane as its attached coil. Energization of the coil thus will tend to move the activating portion along its length and, since the attached leg 10a is perpendicular to the activating portion, the leg 10a will allow this movement while supporting the activating portion in all other directions. The pellet portion must move along its length and at a right angle to the plane of the paper. The leg 10a which is attached and located perpendicular to the pellet portion allows movement in this direction. Each hammer is brought back to its initial position by being rebounded from the paper, ribbon and drum. If desired, it can then be damped to a standstill by passing short pulses in the proper directions through its attached coils. In this manner the magnetic forces on the coil are used to stop the hammer.

While many control circuits are suitable, FIG. 3 illustrates one possible system having 11 number of hammers. A code disc 20, mounted on the shaft 1a of the rotating print drum 1, is interposed between a light source 2 1 and a photosensing device 22. The code disc has eight separate concentric bands. The innermost six bands 20a have sixty-f0ur radial rows of coded indicia, each row corresponding to one of sixty-four type characters 1b on the drum. Six bands are required to produce sixty-four different binary-coded signals corresponding to the sixtyfour type characters on the drum. The next band 20b contains one timing indicia for each row in the inner bands 20a. The outermost band 200 has only one indicia and produces a signal on each cycle of the drum. The photosensing device 22 has eight separate detectors; six character detectors 22a, a timing detector 22b and a cycle detector 220, all of which cooperate with their respective bands on the disc. As each row of type characters approaches the hammers, the character detectors 22a of the photosensing device produce a unique binary-coded signal when energized by light passing through the coded indicia 20a of the disc. A series of pulses is produced by the timing portion 22b of the photosensing device, each pulse indicating one row of characters moving past the photosensing device. The pulses produced by the portion 220 of the photosensing device indicate each full drum cycle.

Cables 23a-n transmit coded input data to comparators 24a-n. The input data indicates the characters to be printed by the hammers 9a-n arranged along the print line at the drum. If the print drum 1 contains sixty-four type characters on its periphery, each of the cables 23a-n contains six data lines, allowing for the binary-coded representation of sixty-four characters. The character indicating binary-coded signals from the photosensing devices are also fed to the comparators over a common cable 25 and branch cables 25a. The common cable 25 and each of the branch cables 25:: also contain six lines. Each comparator receives the data transmitted by one of the cables 23an and the data transmitted by the cable 25. When a match is indicated in a comparator, it supplies a pulse to a corresponding AND gate 2611-41. Each AND gate also receives an input signal from the timing portion 22b of the photosensing device and, upon receiving signals from both of these inputs, provides a FIRE pulse to a hammer driver 27a-n.

The period of delay occurring between energization of the photosensing device and impact of the hammers on the drum is compensated for by having the code disc lead the characters on the drum by an appropriate distance. The output signal from that portion 22c of the photosensing device which indicates a full drum revolution is fed over line 28 to request new data from the data source and over line 29 to request that the paper be advanced so that the next line may be printed.

We claim:

1. In a printer having a hammer mechanism containing at least one hammer towhich is attached an activating coil and magnetic field generating means for providing magnetic lines of force across portions of the activating coils such that the hammers may be selectively activated by selective energization of the coils, the improvement which comprises:

(a) a plurality of spaced pole pieces, portions of an activating coil being interposed between each pair of adjacent pole pieces; and

(b) at least one permanent magnet for each pair of adjacent pole pieces, each magnet being interposed between and abutting a pair of adjacent pole pieces, the opposed abutting surfaces of each magnet being of opposite polarities.

2. The printer as recited in claim 1 wherein the pole 5 pieces and magnets are positioned such that each pole piece is of a single polarity and adjacent pole pieces are of opposite polarities.

3. The printer as recited in claim 2 wherein the magnets are thin members magnetized through their thin dimensions.

4. The printer as recited in claim '3 wherein each magnet is U-shaped and each pair of adjacent pole pieces abut the outside and inside of a U-shaped magnet.

5. The printer as recited in claim 4 wherein:

each pole piece abutting the outside of one of the U- shaped magnets is also U-shaped;

the pole pieces extend past the ends of the U-shaped magnets; and

portions of the activating coils are interposed between those portions of the pole pieces which extend past the ends of the U-shaped magnets.

6. The printer as recited in claim 5 wherein the magnets and pole pieces extend substantially parallel to, and along the length of the print line.

7. The printer as recited in claim 5 wherein essentially one half of the activating coils are located between the pole pieces.

8. The printer as recited in claim 2 wherein:

at least one of the hammers moves within a single plane when activated;

and further comprising:

a member for holding the hammer within the hammer mechanism, the holding member comprising at least one leg which is flexible in directions within the plane.

'9. The printer as recited in claim 8 wherein:

the hammer comprises at least two portions disposed at an angle to each other; and the holding member comprises at least two of the flexible legs, each leg being adapted to. support a diiferent portion of the hammer and being essentially perpendicular to that portion which it supports.

References Cited UNITED STATES PATENTS 2,947,921 8/1960 Watelet 335-306 3,072,045 1/1963 Goin 101 93 3,087,421 4/1963 Irwin et a1 101-93 3,172,352 3/1965 Helms 101-93 HUGH R. CHAMBLEE, Primary Examiner 

